SEQUENCE OF OPERATION
Sequence of Operation- Double Element,
1Line voltage is applied across terminals L1 & L3 of upper thermostat. Likewise, Line voltage is applied to terminal L3 of lower thermostat. ECO in both upper & lower thermostat is closed, so there is voltage at terminal L4 of both thermostats and to one side of both upper & lower elements.
1
ECO
Closed
2
Thermostat closed
at terminal T2
2Tank is cold therefore both thermostats are closed at terminal T2 (calling for heat). The circuit is complete through the upper thermostat only allowing current to flow through the upper element.
3When the upper thermostat is satisfied, it opens at terminal T2 interrupting current flow through upper element, and closes at terminal T4 allowing voltage to pass to terminal L1 of lower thermostat. This completes the circuit through the lower thermostat allowing current flow through lower element.
4When the lower thermostat is satisfied, it opens at terminal T2 interrupting the current flow through the lower element. The system is now in
5The lower thermostat/element combination will generally cycle on and off more often then the upper. In some cases, such as a cold tank or in high demand periods, the upper thermostat will call for heat (opening at terminal T4 and closing at terminal T2) prior to the lower thermostat being satisfied. This will interrupt current flow through the lower thermostat and element and allow current to flow through the upper element only. When the upper thermostat is satisfied, it resumes operation as described in sequence #3 above.
3
Thermostat closed
at terminal T4
Thermostat closed
at terminal T2
5
Thermostat closed
at terminal T2 
Thermostat closed
at terminal T2
ECO |
|
Closed | Thermostat closed |
| at terminal T2 |
4
Thermostat closed
at terminal T4
Thermostat open
at terminal T2
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